DESCRIPTION: The goal of the proposed research is to investigate subtypes of unilateral spatial neglect theoretically, mathematically and neuroanatomically. Traditional accounts of neglect view space and spatial representations as a single homogeneous entity through which attention is directed. These accounts cannot explain a number of recent empiric observations. The central hypothesis driving this investigation is that the nervous system constructs multiple spatial representations, and neglect may occur within these different representations. These hypothesized representations are anchored to the viewer, the environment and the object. We will conduct three sets of experiments in brain damaged patients and normal control subjects. The first set of experiments which addresses viewer centered reference frames, examines the modulation of neglect by changes in the position of the head in relation to the trunk. The second set of experiments, which addresses environment centered reference frames, examines the modulation of neglect by changes in the position of the entire body in relation to the environment. The third set of experiments, which addresses object center neglect, examines modulation of neglect by changes in visual grain and texture in relation to nascent objects. Each set of experiments will focus on modulation by a different modality (proprioception, vestibular sensation and visual texture) to test the central hypothesis of multiple spatial representations. To precisely characterize neglect subtypes we will develop and apply mathematical analyses of data. The first two sets of experiments will use psychophysical power functions and the third experiment will introduce the use of logistic regression to derive sigmoid functions. From a detailed analysis of the anatomy of these patients' brain lesions, we will investigate lateralizing differences in disorders of spatial attention, the anatomic substrate mediating spatial attention in three dimensions, and the neural mediation of functional modularity. In short, the proposed investigations should provide important evidence to advance our understanding of: 1) how input from different sensory modalities contribute to multiple spatial representations, 2) precise mathematical analyses of neglect behavior, and 3) the neural substrates underlying neglect subtypes.